As shown in FIG. 1, a conventional rotary type hermetic compressor includes a housing 1 containing a motor part having a stator and a rotor, a compression part for compressing refrigerant and a lubrication oil pumping part.
Of the motor part, the stator 4 is secured to the housing and the rotor 3 has a shaft 2 with a hollow.
The shaft 2 is journalled by a main bearing 7 and an auxiliary bearing 8 and the compression part thereof is positioned eccentric to the rotating axis of the shaft in a certain amount.
The compression part is located between the main bearing 7 and the auxiliary bearing 8. This compression part includes, as shown in FIG. 2, a cylinder having a refrigerant suction hole 11 formed at an angle with a refrigerant discharge hole formed therein, a roller 10 surrounding the eccentric part of the cylinder and a vane 15 slidably inserted between the suction hole and the discharge hole.
The vane 15 is adapted to maintain contact with the roller by a spring 16.
Accordingly, as shown in FIG. 2, the contact of the roller 10 with the vane and inside of the cylinder provides two enclosed spaces A and B. Of the two spaces A and B, the space in communication with the suction hole 11 is a suction chamber and the space in communication with the discharge hole is a compression chamber.
The compression process of refrigerant for above described construction is explained hereinafter.
Assuming that the rotor 3 rotates in clockwise direction on power supply to the motor part, the shaft secured to the rotor rotates in the same direction. In this time, as the roller surrounding the shaft moves together with the shaft, the contact point of the roller also moves in clockwise direction according to the rotation of the shaft.
By the consequence, as the space A becomes smaller, the refrigerant in the space A becomes compressed more and more.
If the pressure in the space A becomes higher above a preset level following the compression of the refrigerant in the space A, a valve 14 is opened to discharge compressed refrigerant gas.
Each component of the compression part of such a compressor should be finish machined to an extremely close tolerance so as to prevent leakage of refrigerant and therby to achieve a high efficiency of the compressor. To maintain high degree of finish, adequate lubrications on the moving components are required. Further, it is important that the moving components of the compressor are adequately lubricated so as to maintain the dynamic friction to a low level and minimize the friction loss. Finally, sufficient lubrication can minimize heat from friction loss permitting reduction of heat transfer and improvement of compressor efficiency.
Many types of lubrication arrangements are provided in conventional rotary type hermetic compressors.
Generally, the lubrication part of a conventional compressor has such a construction that a hollow shaft is submerged in an oil sump containing lubrication oil therein. The high pressure of refrigerant gas in the sealed housing or the rotating force of a propeller inserted in the hollow of the shaft pumps up lubrication oil in the oil sump through the hollow in the shaft to be sprayed from pumping oil discharge holes 2c formed on the circumference of the shaft to lubrication parts.
Lubrication oil, thus sprayed, drips down after lubrication and collected to the oil sump by gravity.
A few examples of conventional lubrication arrangements using gravity distribution is shown in U.S. Pat. Nos. 4,640,669 and 3,082,937.
In conventional hermetic compressor lubrication arrangements, the compression of gas is carried out at a pressure above 20-30 bars which is discharged out of the sealed housing through a discharge pipe after filling up the sealed housing as well as the oil sump in the lower part of housing.
Though there has been no problem in normal operations of oil lubrication due to the high gas pressure of above 20-30 bars in the oil sump which will carry out the pumping operation without any problem but in case when the back pressure on the lubricating oil in the oil sump is lower than the pressure in the compression chamber, for example when the high pressure is discharged directly through the discharge pipe without filling the housing, the oil pumping can not be carried out easily.
Accordingly, it has been a problem that lubrication in every lubrication part can hardly be expected because lubrication oil can not be reached to every lubrication part without fail and adequate oil can not be delivered to lubrication part because lubrication oil is not delivered under pressure.
And there is the problem of harmful vibration in a hermetic compressor described above caused by the eccentric part in the compression part of the shaft when the shaft rotates in high speed. To solve this problem, conventional compressors have been provided with another eccentric part in one end of the shaft.